It was a major turning point: the next year, he was in Hollywood for Matt Damon and Ben Affleck's Oscar-winning and Steven Spielberg's slavery drama . But he always stayed friends with von Trier, pitching up in , and a, as well as some television work. Only Norwegian director Hans Petter Moland, with whom Skarsgård's worked four times, comes close.

An epic sexual odyssey, affords Skarsgård his biggest role for von Trier since , in what is arguably the director's most talked-about movie in years. For starters, he's used "body double" porn actors to shoot hardcore sex scenes, despite many of these moments being trimmed for the shorter four-hour/two-volume version that's being distributed.

Not that he got to see much of the film's more risqué shooting, with Skarsgård playing a rather passive bystander. The story sees Charlotte Gainsbourg's character, Joe, recount her life as a sex addict, in a series of increasingly explicit flashbacks, to Skarsgård's kindly Seligman. "The two characters are, of course, two sides of Lars von Trier," Skarsgård says. "One is the nerd Lars von Trier, and that's me [Seligman], and the other is the far more interesting and more multi-layered character played by Charlotte."

With Seligman prone to random digressions, comparing Joe's sexual exploits with all manner of odd topics, Skarsgård is swift to point out that the film is more like a fairy tale. "It's not realism we're dealing with," he says. "All Lars von Trier films are fairy tales in a way and you have to adapt to his universe." And like all fairy tales, there's darkness in - not least in Volume II as Joe's encounters become more addictive and brutal.

It's not the first time von Trier has shown sexual penetration (see both and ). But were the actors worried about what they were getting into? "I have no idea what the fears were on the set. You should ask Stacy Martin [who plays the younger Joe] - she's very smart and a very bright girl. It was like Emily Watson in ; that was her first film. And she was very brave about it. I don't know how much she appreciated the presence of my penis but at least she handled it well!"

This is typical of the Gothenburg-born Skarsgård, who has appeared nude many times on film. "I was born naked. I have a very relaxed relationship to my own nakedness and my parents often walked naked in the apartment when I was a small child. I take off my clothes frequently when I get home. It's very hard to make me blush over that." As his eldest son Alexander once confirmed: "I think I was 14 the first time I saw my dad wearing pants. He was always naked."

While Skarsgård was the eldest of five children, he's continued this tradition of sizeable families - producing five sons and one daughter with My, his wife of 32 years (until they divorced in 2007), and two more sons with his new wife, Megan, whom he married in 2009. His first five sons are all actors - with Alexander a Hollywood sex symbol thanks to his role in American vampire TV show . "When I saw my son naked on the front of ," says Skarsgård, "then I realised he's gotten somewhere!"

With Bill, Gustaf, Sam and now Valter also building careers, the idea that he's raised a family of actors would doubtless please his own father, Jan. "My father wanted to become an actor but he wasn't allowed to because his parents didn't think it was a suitable profession." Instead, he became a business executive. "I don't think he ever really liked it."

Skarsgård's parents were humanists and raised him to be - to borrow from the title of his 2010 film with Moland - a somewhat gentle man. "My parents said to me when I was bullied as a kid, they taught me to feel sorry for the bully," he says. "I don't fight. I'm not a violent person. I think I hit one person once in my life in a fight. But I'm no fighter - I don't like it. I'm scared."

Has he ever fought with von Trier? "No, no, no - I'm so much bigger!" (This is true, with the 1.91-metre-tall Skarsgård towering over the 1.70-metre-tall von Trier.)

Skarsgard tasted fame when he was 16, playing "a Swedish Huckleberry Finn character" in the television series. "It was like becoming a rock star [but] my parents were pretty good about it. They made me keep my head," he says.

Later, he joined Stockholm's Royal Dramatic Theatre Company, but it wasn't until he won the best actor award at the Berlin Film Festival in 1982, for , that his international profile began to rise.

A regular in Hollywood and European cinema, he's just finished roles in , with Simon Pegg and Rosamund Pike, Kenneth Branagh's fairy-tale , and a new John le Carré adaptation, . Nonetheless, "I'd still rather be an actor than a star," he says.

Nymphomaniac: Volume I Volume II Volume I Volume II